Attention has been recently directed to a hybrid vehicle which travels by drive force from at least either one of an engine and a motor as part of measures for environmental issues. On such a hybrid vehicle is mounted a capacitor (i.e., a condenser) or the like for accumulating electric power to be supplied to the motor. Japanese Patent Laying-Open No. 2005-061498 discloses a hybrid vehicle having such a battery or such a capacitor mounted thereon.
The hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2005-061498 includes: an engine; a first motor generator for exhibiting both of a function of an electric motor and a function of a power generator, a power distributing mechanism for distributing power of the engine to the first motor generator and a transmission shaft; a second motor generator connected to the transmission shaft, to exhibit both of the function of the electric motor and the function of the power generator; a transmission connected to the transmission shaft, to change and output the rotational speed of the transmission shaft; a drive shaft connected to an output shaft of the transmission via a differential; a drive wheel connected to the drive shaft; and a battery and a capacitor electrically connected to the first motor generator and the second motor generator via inverters, respectively.
In the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2005-061498, electric power accumulated in the battery and the capacitor is electrically discharged to the first motor generator and the second motor generator at the time of the start of the vehicle. In the meantime, regenerative electric power generated in the first motor generator and the second motor generator is electrically charged to the battery and the capacitor at the time of deceleration of the vehicle. The capacitor excellent in input/output characteristics more than the battery is used in a case where a large current is instantaneously generated during the electric charging/discharging. As a consequence, it is possible to suppress any up-sizing of the battery.
On the other hand, when a driver drives forward a vehicle at a standstill on an up-hill road by switching from a brake pedal to an acceleration pedal, the vehicle may be unexpectedly moved backward against an intention of the driver (such a phenomenon is referred to also “slip-down,” but hereinafter simply referred to “reverse”). As soon as the vehicle is started to be reversed, the drive wheels also are started to be rotated in a direction of the reverse of the vehicle. The rotation of the drive wheels is transmitted to the first motor generator and the second motor generator via the drive shaft and the transmission, to thus generate electric power. The generation of the electric power produces torque for suppressing the rotation of the drive wheels (i.e., the reverse of the vehicle). In order to further increase the suppressing torque, it is necessary to efficiently consume the generated electric power at the time of the reverse. In the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2005-061498, the generated electric power at the time of the reverse can be electrically charged to the battery and the capacitor, and therefore, a greater suppressing torque can be expected in comparison with a case of the electric charging only to the battery.
However, in the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2005-061498, the generated electric power at the time of the reverse is electrically charged only to the battery when the capacitor is in a fully electrically charged state at the time of the reverse. Therefore, the smaller suppressing torque makes it difficult to suppress the reverse of the vehicle in comparison with a case of the electric discharging to both of the battery and the capacitor.